In wireless transceiver systems there is a trend toward accommodating an ever increasing number of bands and various receiving modes (multimode) while satisfying the corresponding band and mode requirements. For example, duplex filters of EDGE/WCDMA receivers attempt to satisfy the blocker rejection requirements of both GSM-EDGE and UMTS system modes. A blocker or interferer is an unwanted signal, which tends to block the desired signals in a receiver (RX) by exceeding the linear operating range of the RX circuitry. GSM generally requires approximately 15/25 dB damping of the blockers that are greater than 20 MHz to 80 MHz above and below the reception band, while UTMS generally requires more than 50 dB damping at 20 MHz below the reception band (for the transmit (TX) leakage because of full duplex). In a multimode arrangement, two or more of these requirements may be addressed within the same receiver and/or at the same time. Accordingly, there is a need to combine these various band modes into a single receiver.
In addition, there is a growing need to decrease the costs of such receiver front-ends by reducing the number of components and/or by integrating as many components of these wireless transceivers as possible onto a single semiconductor die/chip. For example, such transmit-receive (TRX) systems are often used in wireless personal communications including cell phones, two-way radios, and PDAs.
Satisfying these multiple requirements (e.g., GSM and UMTS) simultaneously in a conventional approach, may lead to increased insertion loss in the duplex filters for at least some of the multimode bands. In one conventional approach, the GSM reference sensitivity can be impaired enough to cause the architecture to become unsuitable. For these reasons, an external (off-chip) low-noise amplifier (LNA) is often used, because they may provide better performance than the on-chip CMOS TRX, along with an interstage filter to provide additional damping of the blockers and the TX signal.